1. Field of the Invention
The present invention is concerned with novel methods for the catalytic synthesis of polyhalogenated and perhalogenated keto alkenoic acids, such as, for example, halogenated C.sub.5 to C.sub.10 mono-carboxylic acids; from the corresponding saturated keto acids their esters, amides, anhydrides, lactones, acyl halides, and other acidogenic derivatives. More particularly, it pertains to methods of catalytically chlorinating and/or brominating 4-keto-pentanoic acids and their derivatives to obtain acyclic and cyclic olefinic products which contain at least 4 halogen atoms per molecule.
2. Description of the Prior Art
While various investigators have reported the chlorination of 4-keto C.sub.4 to C.sub.10 acids to the mono or dichloro stage, there is no report to date of any direct combined chlorination and dehydrogenation of such acids (or their acidogenic derivatives) to the unsaturated polyhalogenated or perhalogenated stage. As used herein, the terms "polyhalogenated" and "polychlorinated" refer, respectively, to compounds containing at least four halogen atoms per molecule (which may be of the same or of different halogens) and to compounds which contain at least four chlorine atoms per molcule. The terms "perhalogenated" and "perchlorinated" refer, respectively, to compounds in which all of the hydrogen atoms attached to carbon atoms in the molecule are substituted with halogen atoms (which may be of the same or different halogens), and to compounds in which all of the hydrogen atoms attached to carbon atoms are substituted with chlorine atoms. The term "halogen" is intended to include chlorine, bromine or combinations thereof.
A common 4-keto-pentanoic acid, which is available in commerce, is levulinic acid. Early attempts to chlorinate levulinic acid directly resulted only in the production of mono-and dichloro derivatives. [Seissl, Annallen, 249, 288-303 (1888).] A number of polychloro-pentenoyl ketones, acids, acid halides and anhydrides have since been prepared by methods other than by the direct chlorination of levulinic acid [Zincke, Berichte der Deutsche Chemische Gessellschaft, 23, 240, (1890); 24, 916, (1891); 25, 2221, (1892); 26, 506, (1893); and 26, 317, (1893)].
U.S. Pat. No. 3,275,505 does disclose the direct halogenation of levulinic acid. However, the reaction temperatures are between 100.degree. and 125.degree. C and, even with high degrees of halogenation, no more than four atoms of halogen are added per molecule of levulinic acid. Further, there is no conversion of the acid from a saturated to an olefinic compound.